I have a working demo of Zimbra NE with a few accounts (20 to 25) the demo was 60 days which was more or less the time needed to evaluate the product and try to implement it with other systems. The operation will extend more than expected and wanted to continue operating with the same accounts. migrating calendars, tasks and emails to the open version. We need to move to the open version, because now do not approve the expenditure of the NE version.

All you need to do in that case is to run the Zimbra OSS installer on your NE server and it will 'upgrade' to the OSS version, no need for a migration. Block incoming mail on port 25 and make a backup using NE backup tool and a copy of the /opt/zimbra directory structure (you should shutdown Zimbra for this) before the upgrade. When you've run the upgrade script unblock port 25.